1. Technical Field
This invention relates generally to antenna reflector systems and, more particularly, to equalized far-field shaped beam radiation patterns for offset fed oppositely located shaped reflectors generally found on a spacecraft and technique for equalizing same.
2. Discussion
Antenna systems frequently employ a shaped reflector to collimate or focus a beam of energy into a selected shaped beam pattern with high radiation efficiency. Currently, a number of spacecraft systems employ first and second offset fed shaped reflectors on opposite sides of the spacecraft. The first and second offset fed shaped reflectors are conventionally known and described herein as east and west shaped reflectors.
An offset fed geometry is usually selected to minimize mechanical structure and deployment mechanisms that would normally be utilized in a center fed configuration. It is generally required that the offset fed geometry be rotated around the central axis of the spacecraft while at the same time providing for substantially equal far-field shaped beam radiation patterns. In addition, spacecraft systems typically impose the requirement that the east and west shaped reflectors provide substantially equal gain performance for all communication channels provided therewith.
Equalized offset fed east and west shaped reflectors located opposite one another on a spacecraft are usually employed to provide additional communication channels. For instance, the east shaped reflector may provide six channels of communication, while the west shaped reflector provides an additional six different channels of communication. As a result, the spacecraft satellite system is able to communicate within a desired geographical area using an increased number of channels, each of which provide substantially equal shaped beam radiation patterns.
Current spacecraft communications systems typically require that the east and west shaped antenna reflector gain performance be equalized to within 0.5 dB over the geographical area illuminated by the mainlobe. In addition, stringent sidelobe requirements are frequently imposed which further requires superior equalization. The aforementioned stringent equalization requirements help prevent degradation of adjacent channel performance due to antenna characteristics.
The conventional east and west offset fed shaped reflector approach generally requires two different shaped reflectors which have reflective surfaces shaped different from one another to provide equalized far-field shaped beam radiation patterns. These different shapes generally result from rotating the offset fed geometry 180 degrees around the central axis of the spacecraft, while the farfield shaped beam radiation patterns remain substantially the same. Currently, a considerable amount of time and expense is spent equalizing the east and west shaped reflector performance. Some conventional equalization techniques have employed sophisticated computer operated programs to obtain substantially equal far-field shaped beam radiation patterns. However, the offset reflector geometry generally increases the difficulty which results in increased design cycle time in achieving an acceptable degree of equality between the east and west shaped reflector designs.
It is therefore desirable to provide for an enhanced technique for equalizing oppositely located offset fed east and west shaped reflectors. In addition, it is desirable to provide for equalized oppositely located offset fed east and west antenna reflectors which may be more easily designed and formed. Furthermore, it is desirable to provide for such east and west antenna reflectors which may be designed in a less expensive and less timely manner.